Schottky Barrier Research Articles

Effect of the insertion of silver nanoparticles on the performance and electrical features of Ag/SiNWs Schottky diode

In this paper, we studied the effect of the passivation of silicon nanowires (SiNWs) by silver nanoparticles (AgNPs) on the efficiency of Ag/SiNWs/Si Schottky diodes. SiNWs are obtained by one-step Ag-assisted chemical etching method. AgNPs were deposited on SiNWs using an electroless dipping method. Schottky junction devices have been successfully made using silicon nanowires coated with silver nanoparticles. The current–voltage (I-V) characteristics of Ag/AgNPs-SiNWs Schottky diode have been investigated by varying the immersion time in silver nitrate solution from 1 to 5 min. The I-V characteristics presented in logarithmic scale confirmed the domination of SCLC conduction mechanism at high voltage. The ideality factor (n), height of potential barrier (φb) and series resistance (Rs) of diodes are calculated by adopting the Cheung method. Compared to the Ag/SiNWs Schottky junction, the diode that presents AgNPs at the interface shows a significant improvement in electrical parameters. The potential barrier reaches 1.09 eV and the ideality factor is reduced to 2.64 with the presence of AgNPs for an immersion time of 1 min. Norde’s equation has also been used to calculate the series resistance and the potential barrier. The results obtained by Norde method are slightly shifted compared to those found by Cheung functions while the findings concerning the optimization of the immersion time are practically the same.

Effect of AZO seed layers on the ultraviolet photoresponse of Ag/ZnO NRs Schottky junctions

Al-doped ZnO (AZO) thin films with different layers were prepared by sol-gel method. The SEM, XRD and AFM for three layers thin films demonstrates high crystal quality and low roughness. ZnO nanorods arrays (NRs) with different AZO seed layers were fabricated using hydrothermal process, and the effect of AZO seed layers on the structural, optical, and electrical characteristics was investigated. When there are three AZO seed layers present, ZnO NRs exhibit fewer surface states, smaller interface charge transfer resistance (Rce = 6.1 × 103Ωand Rct = 6.6 × 106Ω), longer carrier lifetimes (τe = 4.0 ms), higher carrier concentration (ND = 4.73 × 1019 cm−3), and narrower depletion region width W = 3.1 nm. Under weak UV light 381 nm (5.68 mW/cm2) at a bias −0.5 V, Ag/ZnO NRs Schottky devices with three AZO seed layers display a comparatively strong responsivity 34.64 mA/W. Appropriate AZO seed layers are favorable for highly efficient ZnO NRs-based photoelectric conversion devices.

Resistive switching suppression in metal/Nb:SrTiO3 Schottky contacts prepared by room-temperature pulsed laser deposition

Deepening the understanding of interface-type resistive switching (RS) in metal/oxide heterojunctions is a key step for the development of high-performance memristors and Schottky rectifiers. In this study, we address the role of metallization technique by fabricating prototypical metal/Nb-doped SrTiO3 (M/NSTO) Schottky contacts via pulsed laser deposition (PLD). Ultrathin Pt and Au electrodes are deposited by PLD onto single-crystal (001)-terminated NSTO substrates and interfacial transport is characterized by conventional macroscale methods and nanoscale Ballistic Electron Emission Microscopy. We show that PLD metallization gives Schottky contacts with highly reversible current-voltage characteristics under cyclic polarization. Room-temperature (RT) transport is governed by thermionic emission with Schottky barrier height ϕB(Pt/NSTO)∼0.71−0.75eV , ϕB(Au/NSTO)∼0.70−0.83eV and ideality factors as small as n(Pt/NSTO)∼1.1 and n(Au/NSTO)∼1.6 . RS remains almost completely suppressed upon imposing broad variations of the Nb doping and of the external stimuli (polarization bias, working temperature, ambient air exposure). At the nanoscale, we find that both systems display high spatial homogeneity of ϕB ( ⩽50meV ), which is only partially affected by the NSTO mixed termination ( |ϕB(M/SrO)−ϕB(M/TiO2)|<35meV ). Experimental evidences and theoretical arguments—based on a metal-insulator-semiconductor description of the M/NSTO—indicate that the PLD metallization mitigates interfacial layer effects responsible for RS. This occurs thanks to the reduction of the interfacial layer thickness and to the creation of an effective barrier against the permeation of ambient gas species affecting charge trapping and redox reactions. This description allows to rationalize interfacial aging effects, observed upon several-months-exposure to ambient air, in terms of a slow interfacial re-oxidation. Our work contributes to the fundamental understanding of interface-type RS and demonstrates that RT PLD offers a viable platform for the realization of robust, RS-free NSTO-based Schottky contacts.

Synthesis and mechanism of hierarchical porous Ag/CuxO (x = 1, 2) nanowire hybrids for high photocatalytic degradation

To improve organic pollutant degradation ability, this work aims at designing a novel porous Cu-Ag bimetal hybrid with unique architecture, fertile porosity as well as Schottky junction. Herein, a free-standing hybrid with Ag nanoparticles modified CuxO (x = 1, 2) nanowires in-situ grown on the nanoporous Cu-Ag bimetal network (Ag/CuxO@NP-CuAg) was successfully synthesized by dealloying and then anodizing process. Compared with monometallic CuxO nanowires integrated with nanoporous Cu substrate (CuxO@NPC), the Ag/CuxO@NP-CuAg hybrids with the Ag/CuxO Schottky junction and SPR effect of Ag nanoparticles, are favorable to accelerate the transportation of photo-generated carriers and avoid the recombination of electrons (e-) and holes (h+), thus exhibiting the enhanced photocatalytic performance for RhB. Such remarkable performance is also contributed to the multimodal hierarchical porous structure and the integration design strategy. Moreover, by density functional theory (DFT) calculation, a typical Z-scheme mechanism is proposed to better understand the photocatalytic degradation process. The formation mechanism of the Ag/CuxO nanowires is also investigated.

Physical Modeling of Threshold Voltage Instability in GaN High‐Electron‐Mobility Transistors

The transient heat conduction equation for the 2D electron gas layer in GaN high‐electron‐mobility transistors is developed. The Schottky barrier height and the conduction band offset seen by electrons in the 2D electron gas layer will be reduced due to self‐heating in the 2D electron gas of GaN high‐electron‐mobility transistors via quantum coupling. Such a reduction will lead to a shift in the threshold voltage. To address this issue, an analytical physical model of self‐heating in the 2D electron gas of a GaN high‐electron‐mobility transistor via quantum coupling impacts on its threshold voltage instability is proposed. The proposed model forecasts that the threshold voltage can have an exponentially dependent relation with the reciprocal of the recovery time after the stress voltage is released, as well as dependencies on the square of the drift velocity, the gate voltage, and the surrounding temperature. The experimentally observed threshold voltage shifts of GaN high‐electron‐mobility transistors confirm such dependent relationships predicted by the proposed physical model. This article provides evidence that the combination of self‐heating in the 2D electron gas layer and quantum coupling may be a possible physical origin of the threshold voltage instability in GaN high‐electron‐mobility transistors.

Over 600 V Lateral AlN-on-AlN Schottky Barrier Diodes with Ultra-Low Ideality Factor

Abstract This letter reports the demonstration of lateral AlN Schottky barrier diodes (SBDs) on single-crystal AlN substrates by metalorganic chemical vapor deposition (MOCVD) with an ultra-low ideality factor (η) of 1.65, a high Schottky barrier height of 1.94 eV, a breakdown voltage (BV) of 640 V, and a record high normalized BV by the anode-to-cathode distance (LAC). The device current was dominated by thermionic emission, while most previously reported AlN SBDs suffered from defect-induced current with higher η (&gt;4). This work represents a significant step towards high-performance ultra-wide bandgap AlN-based high-voltage and high-power devices.

P-Type Schottky Contacts for Graphene Adjustable-Barrier Phototransistors

The graphene adjustable-barriers phototransistor is an attractive novel device for potential high speed and high responsivity dual-band photodetection. In this device, graphene is embedded between the semiconductors silicon and germanium. Both n-type and p-type Schottky contacts between graphene and the semiconductors are required for this device. While n-type Schottky contacts are widely investigated, reports about p-type Schottky contacts between graphene and the two involved semiconductors are scarce. In this study, we demonstrate a p-type Schottky contact between graphene and p-germanium. A clear rectification with on–off ratios of close to 103 (±5 V) and a distinct photoresponse at telecommunication wavelengths in the infrared are achieved. Further, p-type silicon is transferred to or deposited on graphene, and we also observe rectification and photoresponse in the visible range for some of these p-type Schottky junctions. These results are an important step toward the realization of functional graphene adjustable-barrier phototransistors.

Flexoelectricity Modulated Electron Transport of 2D Indium Oxide.

The phenomenon of flexoelectricity, wherein mechanical deformation induces alterations in the electron configuration of metal oxides, has emerged as a promising avenue for regulating electron transport. Leveraging this mechanism, stress sensing can be optimized through precise modulation of electron transport. In this study, the electron transport in 2D ultra-smooth In2O3 crystals is modulated via flexoelectricity. By subjecting cubic In2O3 (c-In2O3) crystals to significant strain gradients using an atomic force microscope (AFM) tip, the crystal symmetry is broken, resulting in the separation of positive and negative charge centers. Upon applying nano-scale stress up to 100nN, the output voltage and power values reach their maximum, e.g. 2.2mV and 0.2pW, respectively. The flexoelectric coefficient and flexocoupling coefficient of c-In2O3 are determined as ≈0.49nCm-1 and 0.4V, respectively. More importantly, the sensitivity of the nano-stress sensor upon c-In2O3 flexoelectric effect reaches 20nN, which is four to six orders smaller than that fabricated with other low dimensional materials based on the piezoresistive, capacitive, and piezoelectric effect. Such a deformation-induced polarization modulates the band structure of c-In2O3, significantly reducing the Schottky barrier height (SBH), thereby regulating its electron transport. This finding highlights the potential of flexoelectricity in enabling high-performance nano-stress sensing through precise control of electron transport.

Hollow Co9S8-carbon fiber hierarchical heterojunction with Schottky contacts for tunable microwave absorption

Heterogeneous interface engineering of hollow hierarchical structures with Schottky contacts is an attractive approach for designing light weight and efficient microwave absorption (MA) materials. Herein, hollow Co9S8-carbon fiber (CF) composites were prepared by solvothermal, electrostatic spinning, and pyrolysis methods. CF was used as the main chain and hollow Co9S8 derived from metal-organic frameworks (MOFs) was homogeneously embedded in it, which overcame the difficulties of the traditional template method and effectively avoided the particle agglomeration problem. The interface polarization relaxation process is improved by the construction of Co9S8-CF heterojunction with Schottky contacts, which effectively modulates the dielectric loss. The internal hollow macroporous cavity and CF with lightweight properties enhance the reflection attenuation of the internal cavity. In addition, the electromagnetic characteristics can be flexibly adjusted to achieve the tunable MA performance by varying the reaction parameters. As a result, the Co9S8-CF-3–700 exhibits optimum MA performance, with a reflection loss (RL) of −60.83 dB at 10.85 GHz and a thickness of 2.76 mm. The effective absorption bandwidth (EAB) extends to 5.6 GHz at a thickness of 2.19 mm. This research provides a promising approach to creating light weight and efficient MA materials with potential applications in radar and communication systems.

Modulate the work function of MXene in MXene/InGaN heterojunction for visible light photodetector

MXene/InGaN heterojunction photodetectors with simple structure and superior optoelectronic performance are considered a viable option for optical communication. However, the integration of MXene with InGaN faces the problem of a relatively low Schottky barrier, leading to electron backflow, which hinders the separation of carriers and limits the photoresponse of photodetectors. Herein, high-performance MXene/InGaN heterojunction photodetectors were fabricated, and the work function of Ti3C2TX was modulated to explore its effect on the performance of the photodetectors. The ascorbic acid treatment increased the work function of MXene from 4.20 to 4.34 eV, enhancing the Schottky barrier height of the heterojunction from 0.56 to 0.70 eV. The devices exhibit excellent photoresponse performances, such as a responsivity of 0.133 A W−1 and a specific detectivity of 2.81 × 1011 Jones at −1 V bias, as well as a short rise/decay time of 37.49/110 μs at 0 V bias. Additionally, the photodetectors achieve high stability that can maintain over 95% of the initial value after 3 months. This work indicates the potential for utilizing tunable MXene work function to construct high-performance optoelectronic devices for visible light applications.

Noise and sensitivity analysis of the dielectric modulated reconfigurable SiNW-SBT for biosensor applications

For the first time, we reported the noise and sensitivity analysis of the Dielectric Modulated Reconfigurable Silicon Nanowire-based Schottky Barrier Transistor (DMR SiNW-SBT) for biosensor applications. To validate the simulation, we present experimental calibration of the DMR SiNW-SBT biosensor. The biomolecules having different dielectric constants and charge densities are immobilized in the cavity region under the control gate. These biomolecules modulate the Schottky junction width at the source channel interface and enhance the drain current of the biosensor. The simulation results indicate that the proposed device ION and VTH sensitivity improved by 54.65 % and 85.71 %, respectively, with the state-of-the-art biosensors. Noise analysis shows that the NFmin decreased by 190.32 % and offers a low source impedance of 70Ω, which minimizes signal loss and distortion. Additionally, we investigate the linearity parameters that outperformed the FET-based biosensors. The gm3 experiences a reduction of 123.21 %, while the VIP3 sees an increase of 7.87 % and the IIP3 shows a rise of 7.21 %. Furthermore, we have conducted device optimization by varying the cavity length and thickness. We also outline potential fabrication steps for the DMR SiNW-SBT biosensor. Thus, results show that the proposed biosensor emerges as a promising candidate for advanced biosensing applications with high sensitivity, enhanced linearity, and robust noise resilience.

Significantly enhanced reliability in defect-engineered BaTi1-xMgxO3 ceramics

BaTiO3-based ceramic is considered to be a fascinating dielectric material with high reliability for ultra-thin multilayer ceramic capacitors (MLCC). Here, we fabricated a series of acceptor-doped BaTiO3 (Mg: 0.2, 0.5, 1.0, 1.5, 2.0, and 5.0 mol%) ceramics with Al2O3 and SiO2 as sintering additives. With an increase in Mg concentration, the insulation resistance of the BaTi1-xMgxO3 ceramics initially increases and then decreases, in which the 0.5 mol% Mg-doped ceramic achieves superior degradation behavior. The reason is that with the incorporation of the acceptor ion Mg2+, the charge compensation mechanism in the system changes. Initially, barium vacancy is generated, which is gradually dominated by oxygen vacancy. Analysis indicates that the segregation of the acceptor state barium vacancy to the grain boundary increases the schottky barrier of the grain boundary, while the gradual increase of the donor state oxygen vacancy reduces the reliability of the ceramic. This study provides a comprehensive overview illustrating the significant role of point defects in the potential barrier of the grain boundary in acceptor-doped BaTiO3 ceramics. It identifies a pathway to achieve high reliability in BaTiO3-based MLCC.

Enhanced resistive switching behaviors of organic resistive random access memory devices by adding polyethyleneimine interlayer

Organic nonvolatile memory devices have garnered significant attention as next-generation electrical memory units owing to their potential for low-cost and straightforward fabrication through a solution process. In this study, we successfully fabricated fully solution-processed organic resistive random access memory (RRAM) devices using poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the resistive switching (RS) layer, with poly(3,4-ethylene-dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) employed as the top electrode. Additionally, to enhance performance further, a polyethyleneimine (PEIE) interlayer was introduced between the bottom electrode and the P3HT:PCBM RS layer. The resulting organic RRAM devices with the PEIE interlayer exhibited bipolar resistive switching, with improved endurance increasing from 50 to 100 cycles, a retention time of 103 s, and a low SET voltage of 0.7 V. The organic RRAM devices featuring the PEIE interlayer demonstrated superior RS performance attributed to the higher Schottky barrier at the interface between the bottom electrode and the active switching layer, creating an asymmetric structure. I-V curve fitting confirmed that the potential switching mechanism involved Schottky emission in the high-resistance state and Ohmic conduction in the low-resistance state. Our findings suggest that organic RRAM devices with a PEIE interlayer hold promise for stable nonvolatile memory applications.

Lateral 1200V SiC schottky barrier diode with single event burnout tolerance

For a power device to be used in space, it must be able to recover from a single event effect caused by heavy ion radiation. Conventional vertical silicon carbide (SiC) power devices such as automotive diodes and MOSFETs, can only meet this requirement if they are heavily derated, a 1200 V device typically unusable above 200 V. In this paper, a lateral RESURF Schottky diode has been designed in TCAD simulation using a radiation-hard (rad-hard) by design methodology. By preventing anode-to-cathode shorting that occurs in a vertical drift region, the lateral design is shown to recover after a heavy ion traverses the device with a linear energy transfer (LET) of 60 MeV·cm2/mg, while the device is blocking 1200 V. The design splits the drift region into a higher doping zone closer to the cathode (Zone 2) of 1.5×1017 cm−3 and a lower doping zone closer to the anode (Zone 1) of 1×1016 cm−3. The electric field spikes were reduced while the device was recovering. This design keeps the local temperature in the device to under 1000 K if the heavy ion penetrates the device in a direction perpendicular to the surface. Other entry positions and directions are also simulated and a maximum temperature of 1733 K occurs when the ion path is horizontal, entering at 1 μm below the surface. However, this temperature peak occurs at the cathode, which is not expected to lead to lasting leakage damage. A deep P+ pillar embedded into the anode acts as a collector for holes generated during the single event. Simulations show that a deeper P+ pillar, to a depth of up to 5 μm, reduces the hole density in the N-drift region and P-epi layer during recovery. This also allows the Zone 1 doping to be increased to as much as 5×1016 cm−3, thereby reducing on-state losses.

Prospects of silicide contacts for silicon quantum electronic devices

Metal contacts in semiconductor quantum electronic devices can offer advantages over doped contacts, primarily due to their reduced fabrication complexity and lower temperature requirements during processing. Some metals can also facilitate ambipolar device operation or form superconducting contacts. Furthermore, a sharp metal–semiconductor interface allows for contact placement in close proximity to the active device area avoiding damage caused by dopant implantation. However, in the case of gate-defined quantum dots in intrinsic silicon, the formation of a Schottky barrier at the silicon–metal interface can lead to large, nonlinear contact resistances at cryogenic temperatures. We investigate this issue by examining hole transport through metal oxide-semiconductor transistors with platinum silicide contacts on intrinsic silicon substrates. We extract the contact and channel resistances as a function of temperature and improve the cryogenic conductance of the device by more than an order of magnitude by implementing meander-shaped contacts. In addition, we observe signatures of enhanced transport through localized defect states, which we attribute to platinum clusters in the depletion region of the Schottky contacts that form during the silicidation process. These results showcase the prospects of silicide contacts in the context of cryogenic quantum devices and address associated challenges.

Fast and scalable fabrication of Ag/TiO2 nanostructured substrates for enhanced plasmonic sensing and photocatalytic applications

Here we propose a fast and scalable (up to 3 min for 6 × 1 cm size substrate) innovative approach to fabricate coral-shaped TiO2 nanostructured substrates based on thermal oxidation of titanium foil followed by deposition of Ag nanoparticles for bifunctional sensing and photocatalysis. Comprehensive studies on the morphology, crystal structure, stoichiometry, optical, and electronic properties of these nanostructures reveal the formation of a Schottky barrier at the Ag/TiO2 interface. This interface alters the electronic structure of the Ag/TiO2 nanosystem, retaining the plasmonic properties of Ag nanoparticles while enhancing their catalytic activity. The SERS performance and photocatalytic activity of Ag/TiO2 nanostructures are demonstrated by the test analyte Rhodamine 6G detection down to concentrations of 10-12 M and acceleration of its degradation under simulated sunlight by 5.8 times. Tests with tetracycline water solutions indicate a nanomolar detection limit and 4.4-fold increase in degradation rate. The proposed Ag/TiO2 nanostructures are prospective for creation of low-cost bifunctional platforms for the sensitive detection of organic residues in water as well as their fast neutralization under solar light.

SiC and Si detectors comparison for high carbon energy spectrometry

An innovative SiC Schottky junction and a traditional p-n Si surface barrier detector have been compared to detect carbon ions with MeVs kinetic energy. To this, a comparison was performed during Rutherford backscattering spectrometry (RBS) using 2–10 MeV carbon ion beams. The energy resolution and detection efficiency for RBS analysis using the two detectors and their detection electronics are presented.The detector parameters dependencies on the surface passivating layers, ion energy and current dependence, ion penetration depth, detection efficiency, energy resolution, and others are discussed.The comparison of RBS analysis with SiC and Si is investigated highlighting the advantages and disadvantages of using SiC with respect to the traditional Si surface barrier detectors. The two detectors employed for proton, helium and carbon RBS spectrometry of different targets have been also compared on the base of the literature data.

Research on the robust electrical contact properties and favorable transport characteristics of two-dimensional WB4/MoSi2N4 van der Waals heterostructures

Ensuring optimal interface contact performance is crucial for achieving low-resistance ohmic contact in the design of two-dimensional (2D) electronic devices. In this study, we systematically investigate the contact properties of van der Waals (vdW) heterojunctions formed by compositing the semi-metal WB4 with Dirac cones and the semiconductor MoSi2N4 through first-principles calculations. A thorough investigation has been carried out on the electronic structure and transport characteristics at the interface. Our research findings indicate that the WB4/MoSi2N4 combination demonstrates robust ohmic contact performance, maintaining ohmic or near-ohmic p-type Schottky contacts over a wide range when exposed to electric field, varying layer spacing, and biaxial strain. This unique characteristic is associated with the Fermi level pinning (FLP), where there are gap states present at the interface. Here, the FLP plays a positive role in maintaining ohmic contact. In addition, different derivatives of MoSi2N4 are combined with WB4 to create heterostructures and study the changes in contact performance. Our research shows that the robust ohmic contact of WB4/MoSi2N4 will have excellent prospects for application in future electronic devices.

Engineering Ultrathin CuxS Layer on Planar Sb2S3 Photocathode to Enhance Photoelectrochemical Transformation.

Sb2S3 has been extensively used as light absorber for photoelectrochemical cell. However, its p-type nature may result in the formation of Schottky junction with substrates, thus hindering the collection of photogenerated holes. Herein, an ultrathin CuxS layer is successfully engineered as the bottom junction for Sb2S3 for the first time. Capitalizing on its impressive electrical properties and superior optical properties, the CuxS layer exhibits a high work function of 4.90 eV, which causes the upward band bending of p-type Sb2S3, forming a hole-transparent structure with ohmic contact. The transparency of the ultrathin CuxS layer enables back-illumination of the Sb2S3/CuxS platform, facilitating the integration of intricate catalyst layers for photoelectrochemical transformation. When modified with Pt nanoparticles, the photocurrent density reaches -5.38 mA cm-2 at 0 V vs. RHE, marking a fourfold increase compared to the photocathode without CuxS layer. When introducing a molecular hybrid TC-CoPc@carbon black, a remarkable average photocurrent density of -0.44 mA cm-2 at the overpotential of 0 V is obtained for CO2 reduction reaction, while the photocurrent density is less than -0.03 mA cm-2 without CuxS.

The Contact Properties of Monolayer and Multilayer MoS2-Metal van der Waals Interfaces

The contact resistance formed between MoS2 and metal electrodes plays a key role in MoS2-based electronic devices. The Schottky barrier height (SBH) is a crucial parameter for determining the contact resistance. However, the SBH is difficult to modulate because of the strong Fermi-level pinning (FLP) at MoS2-metal interfaces. Here, we investigate the FLP effect and the contact types of monolayer and multilayer MoS2-metal van der Waals (vdW) interfaces using density functional theory (DFT) calculations based on Perdew–Burke–Ernzerhof (PBE) level. It has been demonstrated that, compared with monolayer MoS2-metal close interfaces, the FLP effect can be significantly reduced in monolayer MoS2-metal vdW interfaces. Furthermore, as the layer number of MoS2 increases from 1L to 4L, the FLP effect is first weakened and then increased, which can be attributed to the charge redistribution at the MoS2-metal and MoS2-MoS2 interfaces. In addition, the p-type Schottky contact can be achieved in 1L–4L MoS2-Pt, 3L MoS2-Au, and 2L–3L MoS2-Pd vdW interfaces, which is useful for realizing complementary metal oxide semiconductor (CMOS) logic circuits. These findings indicated that the FLP and contact types can be effectively modulated at MoS2-metal vdW interfaces by selecting the layer number of MoS2.